Since 2002 Perimeter Institute has been recording seminars, conference talks, public outreach events such as talks from top scientists using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities.
Recordings of events in these areas are all available and On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
Accessibly by anyone with internet, Perimeter aims to share the power and wonder of science with this free library.
In quantum spin systems, the existence of a spectral gap above the ground state has strong implications for the low-energy physics. We survey recent results establishing spectral gaps in various frustration-free spin systems by verifying finite-size criteria. The talk is based on collaborations with Abdul-Rahman, Lucia, Mozgunov, Nachtergaele, Sandvik, Yang, Young, and Wang.
I will explain how dark energy in cosmology could arise from the
noisy diffusion of energy from the low energy degrees of freedom of matter (described in terms of QFT)
to the fundamental Planckian granularity (expected from quantum gravity). This
perspective leads to a natural model resolving the fine tuning problem associated to the small
value of the cosmological constant. However, recent observations suggest that the dark energy
component in our universe might not be constant and should instead have grown from the recombination time to the present.
Analytic renormalisation "à la Speer" using a multivariable approach typically leads to meromorphic germs in several variables whose poles are linear. In particular, Feynman integrals, multizeta functions and their generalisations, namely discrete sums on cones and discrete sums associated with trees give rise to meromorphic germs at zero with linear poles. We shall present a multivariable renormalisation scheme which amounts to a minimal subtraction scheme in several variables.